Enhanced thickness fabric and method of making same

ABSTRACT

The present invention provides thickened fabrics and reinforcements for use as a spacer or reinforcement for a matrix system. The fabric includes in a first embodiment a woven fabric comprising weft and warp yarns containing glass fibers. A portion of the weft yarns are undulated, resulting in an increased thickness for the fabric. The fabric is coated with a polymeric resin or bonding agent, for substantially binding the weft yarns in the undulated condition. This invention also includes methods for making such fabric by increasing the thickness of a woven or non-woven material by such methods as applying tension during weaving operations, or using unbalanced yarns.

FIELD OF THE INVENTION

The present invention relates to fabrics useful as reinforcements, andespecially, fabric manufacturing methods for manipulating fibers toachieve selected properties.

BACKGROUND OF THE INVENTION

A composite material can be defined as a macroscopic combination of twoor more distinct materials, having a recognizable interface betweenthem. Because composites are usually used for their structuralproperties, they often refer to materials that contain a reinforcement,such as fibers or particles, supported by a binder or matrix material.The discontinuous fibers or particles are generally stiffer and strongerthan the continuous matrix phase, which can be a polymer, mastic orhydraulic setting material, for example.

Fiber reinforced composites can be further divided into those containingdiscontinuous or continuous fibers. There is a tremendous potentialadvantage in strength-to-weight and stiffness-to-weight ratios of fiberreinforced composites over conventional materials. Their desirableproperties can be obtained when the fibers are embedded in a matrix thatbinds them together, transfers the load to and between the fibers, andprotects the fibers from environments and handling.

Glass fiber reinforced organic matrix composites are the most familiarand widely used, and have had extensive application in industrial,consumer and military markets. Carbon fiber reinforced resin matrixcomposites are, by far, the most commonly applied advanced compositesfor a number of reasons. They offer extremely high specific properties,high quality materials that are readily available, reproducible materialforms, increasing favorable cost projections, and comparative ease ofmanufacturing. Composites reinforced with aramid, other organics, andboron fibers, and with silicon-carbide, alumina, and other ceramicfibers, are also used.

Once continuous high strength fibers have been produced, they areusually converted into a form suitable for their intended compositeapplication. The major finished forms are continuous roving, wovenroving, fiberglass mat, chopped strand, and yarns for textileapplications. Woven roving is produced by weaving fiberglass or carbonrovings, for example, into a fabric form. This yields a coarse productthat may be used in many hand lay-up and panel molding processes toproduce fiber reinforced plastics, mastics, roofing materials, andhydraulic setting boards. Many weave configurations are available,depending upon the requirements of the composite. Plain or twill weavesprovide strength in both directions, while a unidirectionally stitchedor knitted fabric provides strength primarily in one dimension. Manynovel fabrics are currently available, including biaxial, double biasand triaxial weaves for special applications.

Fiber glass yarns are typically converted to fabric form by conventionalweaving operations. Looms of various kinds are used in the industry, butthe air-jet loom is the most popular. The major characteristics of afabric include its style or weave pattern, fabric count, and theconstruction of warp yarns and fill yarns. Together, thesecharacteristics determine fabric properties, such as drapability andperformance in the final composite. The fabric count identifies thenumber of warp and fill yarns per inch. Warp yarns run parallel to themachine direction, and fill yarns are perpendicular.

Texturizing is a process in which the textile yarn is subject to anair-jet that impinges on its surface to make the yarn “fluffy”. Theair-jet causes the surface filaments to break at random, giving the yarna bulkier appearance. Carding is a process that makes staple fiber glassyarn from continuous yarn. Texturized or carded yarn absorbs much moreresin or other matrix material, than unmodified yarn, and increases theresin-to-glass ratio in the final composite. Aramid and glass fibers arealso known to be processed into needle-punched felts, whichadditionally, improves the resin absorption and/or fluffiness of thefabric.

While needling, texturizing and carding have provided improvedproperties and more interesting dimensional characteristics for fabric,there remains a present need for manipulating yarns in a fabric toachieve even greater fabric thicknesses.

SUMMARY OF THE INVENTION

In a first embodiment of this invention, a fabric is provided includingan oriented layer containing polymeric or glass fibers wherein at leasta portion of the fibers are mechanically manipulated to increase thelayer's thickness by at least about 50%. These manipulated fibers aretreated with a polymeric coating so as to retain the layer's increasedthickness.

The present invention provides woven, knit, braided, and/or scrim-likeconstructions which are, preferably, fairly “open”, having hole sizesgreater than about 1 mm, and preferably, about 0.02 to more than 4.0square inches. Such an open construction allows matrix material toeasily penetrate the fabric and encapsulate the fibers. The presentinvention provides significantly enhanced thickness versus typical highperformance fabric reinforcements of similar construction. Suchthicknesses have been difficult to achieve in a cost effective way bynormal means of fabric formation. The fabric should be able to withstandsix (6) pounds per square foot of matrix loading without significantdeformation.

In a preferred process for this invention, a woven, knitted, braided orscrim-like fabric comprising weft and warp yarns containing glass fibersis provided. A tensile force is applied to the warp yarns, whereby aportion of the weft yarns becomes undulated, resulting in an increasedthickness for the fabric. The fabric is then bound together with abonding agent, such as a polymeric resin, whereby the undulated weftyarns become substantially fixed. By exploiting certain constructions,such as a “leno weave”, and by coating and drying the product in situ,such as on a tenter frame, whereby the width of the fabric can becontrolled, a fabric of much greater thickness can be produced in acontrolled and repeatable way.

Using a leno weave fabric as an example, this invention takes advantageof the construction of weft yarns inserted through the twisted warpyarns at regular intervals, and which are locked in place. When tensionis applied to the warp yarns, they are inclined to untwist themselves,creating a torque effect on the weft yarns. As each warp yarn untwists,the combined torque effect creates a weft yarn that assumes a generallysinusoidal profile when viewed in the plane of the fabric. The thicknessof the fabric thus increases about 0.5 to 100 fold at the cost of asmall loss in the width of the fabric.

It has been found that for this thickness increase and width to beenhanced, controlled and reproducible, it is preferred that the productbe coated and dried on the fabric making equipment, and held inposition, such as by a tenter frame or by the use of tenter frame with“clips”. The tenter frame functions to apply the necessary tension tothe warp yarns of the fabric to induce the torque effect. The clips holdthe edges of the fabric as it runs through the coating line and dryingoven, and they are adjustable to add or subtract width, as needed.Applying high tension and allowing the width of the fabric to decrease,via the clips, can, in the preferred embodiment, increase the thicknessof the fabric via the torque effect of the warp yarns. The manufactureof the thickened fabric is not limited to tenter frames equipped withclips. “Clipless” drying systems can be used with slightly morevariation in dimensional stability.

Coating selection is important for the purposes of this invention. Inorder for the weft yarns to hold their sinusoidal shape, the coatingmust be somewhat rigid and resist softening in matrix materials,although it is envisioned that the matrix material and the coating canbe the same or different materials. Suitable polymers includestyrene/butadiene and styrene acrylate polymers of high styrene content.E and A/R glass are preferred fibers for the fabrics.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate preferred embodiments of theinvention, as well as other information pertinent to the disclosure, inwhich:

FIG. 1 is a top plan view of a fabric of this invention prior to fibermanipulation;

FIG. 2 is a front plan view of the fabric of FIG. 1;

FIG. 3 is a front plan view of the fabric of FIG. 1 after manipulationof the fibers to increase fabric thickness;

FIG. 4 is a magnified view of a cross over point for the manipulatedfabric of FIG. 3; and

FIG. 5 is a front perspective view of a preferred manufacturingembodiment in which the fabric of FIG. 1 is held by clip chains of atenter frame.

DETAILED DESCRIPTION OF THE INVENTION

This invention provides fabric constructions useful in many end-useapplications, including: polymer matrix composites, soil reinforcement,road, asphalt and mastic reinforcement, cement and gypsum boards, tileunderlayment, drainage mats or systems, roofing membrane and shingles,medical applications such as fiberglass casts, bandages, orthopedicapplications, etc., and textile and carpet applications. In suchapplications, the fabric can be embedded or applied to contact a surfaceof a matrix, or both.

Defined Terms

Composite facing material. Two or more layers of the same or differentmaterials including two or more layers of fabrics, cloth, knits, mats,wovens, non-wovens and/or scrims, for example.

Fabric. Woven or non-woven flexible materials, such as tissues, cloths,knits, weaves, carded tissue, spun-bonded and point-bonded non-wovens,needled or braided materials.

Fiber. A general term used to refer to filamentary materials. Often,fiber is used synonymously with filament. It is generally accepted thata filament routinely has a finite length that is at least 100 times itsdiameter. In most cases, it is prepared by drawing from a molten bath,spinning, or by deposition on a substrate.

Filament. The smallest unit of a fibrous material. The basic unitsformed during drawing and spinning, which are gathered into strands offiber for use in composites. Filaments usually are of extreme length andvery small diameter. Some textile filaments can function as a yarn whenthey are of sufficient strength and flexibility.

Glass. An inorganic product of fusion that has cooled to a rigidcondition without crystallizing. Glass is typically hard and relativelybrittle, and has a conchoidal fracture.

Glass cloth. An oriented fabric which can be woven, knitted, needled, orbraided glass fiber material, for example.

Glass fiber. A fiber spun from an inorganic product of fusion that hascooled to a rigid condition without crystallizing.

Glass Filament. A form of glass that has been drawn to a small diameterand long lengths.

Knitted fabrics. Fabrics produced by interlooping chains of filaments,roving or yarn.

Mat. A fibrous material consisting of randomly oriented choppedfilaments, short fibers, or swirled filaments loosely held together witha binder.

Roving. A number of yarns, strands, tows, or ends collected into aparallel bundle with little or no twist.

Tensile strength. The maximum load or force per unit cross-sectionalarea, within the gage length, of the specimen. The pulling stressrequired to break a given specimen. (See ASTM D579 and D3039).

Tex. Linear density (or gauge) of a fiber expressed in grams per 1000meters.

Textile fibers. Fibers or filaments that can be processed into yarn ormade into a fabric by interlacing in a variety of methods, includingweaving, knitting and braiding.

Viscosity. The property of resistance to flow exhibited within the bodyof a material, expressed in terms of the relationship between appliedshearing stress and resulting rate of strain in shear. Viscosity isusually taken to mean Newtonian viscosity, in which case the ratio ofsheathing stress to the rate of shearing strain is constant. Innon-Newtonian behavior, the ratio varies with the shearing stress. Suchratios are often called the apparent viscosities at the correspondingshearing stresses. Viscosity is measured in terms of flow in Pa's (P),with water as the base standard (value of 1.0). The higher the number,the less flow.

Warp. The yarn, fiber or roving running lengthwise in a woven fabric. Agroup of yarns, fibers or roving in long lengths and approximatelyparallel.

Weave. The particular manner in which a fabric is formed by interlacingyarns, fibers or roving. Usually assigned a style number.

Weft. The transverse threads or fibers in a woven fabric. Those fibersrunning perpendicular to the warp. Also called fill, filling yarn orwoof.

Woven fabric. A material (usually a planar structure) constructed byinterlacing yarns, fibers, roving or filaments, to form such fabricpatterns, such as plain, harness satin, or leno weaves.

Woven roving. A heavy glass fiber fabric made by weaving roving or yarnbundles.

Yarn. An assemblage of twisted filaments, fibers, or strands, eithernatural or manufactured, to form a continuous length that is suitablefor use in weaving or interweaving into textile materials.

Zero-twist-yarn. A lightweight roving, i.e., a strand of near zero twistwith linear densities and filament diameters typical of fiberglass yarn(but substantially without twist).

DETAILED DESCRIPTION OF THE INVENTION

With reference to the Figures, and particularly to FIGS. 1-5 thereof,there is depicted a fabric 101. Needled, woven, knitted and compositematerials are preferred because of their impressive strength-to-weightratio and, in the case of wovens and knits, their ability to form weftand warp yarn patterns which can be manipulated into the thickenedfabric structures of this invention. A thickened fabric is producedwhich includes an open-woven layer comprising high-strength non-metallicweft and warp yarns, whereby a portion of the yarns are mechanicallymanipulated to increase the fabric's thickness by at least about 50%. Infurther embodiments of this invention, a leno weave fabric consisting ofwarp (machine direction yarns), twisted around weft yarns (cross-machinedirection yarns) twist around one another. Weft yarns are insertedthrough the twisted warp yarns at regular intervals and are locked inplace. When tension is applied to the warp yarns they are inclined tountwist themselves, thus creating a torque effect on the weft yarns. Aseach warp yarn untwists, the combined torque effect creates a weft yarnthat assumes a sinusoidal profile when viewed in the plane of thefabric. The thickness of the fabric thus increases, with only a smallloss in the width of the fabric. Such a “thickening” effect can also beproduced with an “unbalanced” fabric construction, such as when thecombined weight of the warp yarns is greater than the combined weight ofthe weft yarns, so the ability of the weft yarns to resist deformationdue to torque is reduced. Another way to accomplish thickening is to useheavier warp yarn, and less of them in the warp direction. This createsgreater tension per warp yard and a wider span of weft yarn for thetensile force to act upon. The result is an increased torque effect,also under normal manufacturing conditions, with an accompanyingincrease in fabric thickness. While the fabric of this invention cancontain fibers and filaments of organic and inorganic materials, such asglass, olefin (such as polyethylene, polystyrene and polypropylene),Kevlar®, graphite, rayon, polyester, carbon, ceramic fibers, orcombinations thereof, such as glass polyester blends or Twintex®glass-olefin (polypropylene or polyethylene) composite, available fromCompanie de Saint-Gobain, France. Of these types of fibers andfilaments, glass compositions are the most desirable for their fireresistance, low cost and high mechanical strength properties.

Glass Composition

Although a number of glass compositions have been developed, only a feware used commercially to create continuous glass fibers. The four mainglasses used are high alkali-resistant (AR-glass), electrical grade(E-glass), a modified E-glass that is chemically resistant (ECR-glass),and high strength (S-glass). The representative chemical compositions ofthese four glasses are given in Table 1 TABLE 1 Glass compositionMaterial, wt % Total Calcium Boric Calcium Zirconium minor Glass typeSilica Alumina oxide Magnesia oxide Soda fluoride Oxide oxides E-glass54 14 20.5 0.5 8 1 1 — 1 A-glass 72 1 8 4 — 14 — — 1 ECR-glass 61 11 223 — 0.6 — — 2.4 S-glass 64 25 — 10 — 0.3 — — 0.7 AR-glass 62 .8 5.6 — —14.8 — 16.7 0.1 (Chem-FIL ®)

The inherent properties of the four glass fibers having thesecompositions are given in Table 2. TABLE 2 Inherent properties of glassfibers Tensile Tensile Coefficient of Liquidus Specific strength modulusthermal expansion, Dielectric temperature gravity MPa Ksi GPa 10⁶ psi10⁻⁶/K constant(a) ° C. ° F. E-glass 2.58 3450 500 72.5 10.5 5.0 6.31065 1950 A-glass 2.50 3040 440 69.0 10.0 8.6 6.9  996 1825 ECR-glass2.62 3625 525 72.5 10.5 5.0 6.5 1204 2200 S-glass 2.48 4590 665 86.012.5 5.6 5.1 1454 2650(a)At 20° C. (72° F.) and 1 MHZ. Source: Ref 4Glass Melting and Forming

The conversion of molten glass in the forehearth into continuous glassfibers is basically an attenuation process. The molten glass flowsthrough a platinum-rhodium alloy bushing with a large number of holes ortips (400 to 8000, in typical production). The bushing is heatedelectrically, and the heat is controlled very precisely to maintain aconstant glass viscosity. The fibers are drawn down and cooled rapidlyas they exit the bushing. A sizing is then applied to the surface of thefibers by passing them over an applicator that continually rotatesthrough the sizing bath to maintain a thin film through which the glassfilaments pass. After the sizing is applied, the filaments are gatheredinto a strand before approaching the take-up device. If smaller bundlesof filaments (split strands) are required, multiple gathering devices(often called shoes) are used.

The attenuation rate, and therefore the final filament diameter, iscontrolled by the take-up device. Fiber diameter is also impacted bybushing temperature, glass viscosity, and the pressure head over thebushing. The most widely used take-up device is the forming winder,which employs a rotating collet and a traverse mechanism to distributethe strand in a random manner as the forming package grows in diameter.This facilitates strand removal from the package in subsequentprocessing steps, such as roving or chopping. The forming packages aredried and transferred to the specific fabrication area for conversioninto the finished fiberglass roving, mat, chopped strand, or otherproduct. In recent years, processes have been developed to producefinished roving or chopped products directly during forming, thusleading to the term direct draw roving or direct chopped strand.

Fabrication Process

Once the continuous glass fibers have been produced they must beconverted into a suitable form for their intended application. The majorfinished forms are continuous roving, woven roving, fiberglass mat,chopped strand, and yarns for textile applications. Yarns are used inmany applications of this invention.

Fiberglass roving is produced by collecting a bundle of strands into asingle large strand, which is wound into a stable, cylindrical package.This is called a multi-end roving process. The process begins by placinga number of oven-dried forming packages into a creel. The ends are thengathered together under tension and collected on a precision rovingwinder that has constant traverse-to-winding ratio, called the waywind.

Rovings are used in many applications of this invention. Woven roving isproduced by weaving fiberglass roving into a fabric form. This yields acoarse product. The course surface is ideal for polymer matrixcomposites, cement board, road patch, soil reinforcement, and adhesiveapplications, since these materials can bind to the coarse fiberseasily. Plain or twill weaves are less rough, thereby being easier tohandle without protective gloves, but will absorb matrices and adhesive.They also provide strength in both directions, while a unidirectionallystitched or knitted fabric provides strength primarily in one dimension.Many novel fabrics are currently available, including biaxial, doublebias, and triaxial weaves for special applications.

Combinations of fiberglass mat, scrim, chopped fibers and woven or knitfilaments or roving can also be used for the preferred reinforcingthickened fabric constructions. The appropriate weights of fiberglassmat (usually chopped-strand mat) and woven roving filaments or loosechopped fibers are either bound together with a chemical binder ormechanically knit, needled, felted or stitched together. One suchcombination would be a fiberglass and/or resin fiber mat or scrimlayered with chopped glass or resin fibers and then needled, felted orstitched together.

The yarns of the facing layers of this invention can be made byconventional means. Fine-fiber strands of yarn from the formingoperation can be air dried on forming tubes to provide sufficientintegrity to undergo a twisting operation. Twist provides additionalintegrity to yarn before it is subjected to the weaving process, atypical twist consisting of up to one turn per inch. In many instancesheavier yarns are needed for the weaving operation. This is normallyaccomplished by twisting together two or more single strands, followedby a plying operation. Plying essentially involves retwisting thetwisted strands in the opposite direction from the original twist. Thetwo types of twist normally used are known as S and Z, which indicatethe direction in which the twisting is done. Usually, two or morestrands twisted together with an S twist are plied with a Z twist inorder to give a balanced yarn. Thus, the yarn properties, such asstrength, bundle diameter, and yield, can be manipulated by the twistingand plying operations. Fiberglass yarns are converted to fabric form byconventional weaving operations. Looms of various kinds are used in theindustry, but the air jet loom is the most popular.

Zero twist-yarns may also be used. This input can offer the ease ofspreading of (twistless) roving with the coverage of fine-filamentyarns. The number of filaments per strand used directly affect theporosity and are related to yarn weight as follows: n=(490×Tex)/d²,where “d” is the individual filament diameter expressed in microns.Thus, if the roving with coarse filaments can be replaced with near zerotwist yarn with filaments half the diameter, then the number offilaments increases by a factor of 4 at the same strand Tex.

The major characteristics of the woven embodiments of this inventioninclude its style or weave pattern, fabric count, and the constructionof warp yarn and fill yarn. Together, these characteristics determinefabric properties such as drapability. The fabric count identifies thenumber of warp and fill or weft yarns per inch. Warp yarns run parallelto the machine direction, and weft yarns are perpendicular.

There are basically four weave patterns: plain, basket, twill, andsatin. Plain weave is the simplest form, in which one warp yarninterlaces over and under one fill yarn. Basket weave has two or morewarp yarns interlacing over and under two or more fill yarns. Twillweave has one or more warp yarns over at least two fill yarns. Satinweave (crowfoot) consists of one warp yarn interfacing over three andunder one fill yarn, to give an irregular pattern in the fabric. Theeight harness satin weave is a special case, in which one warp yarninterlaces over seven and under one fill yarn to give an irregularpattern. In fabricating a board, the satin weave gives the bestconformity to complex contours, such as around corners, followed indescending order by twill, basket, and plain weaves.

Texturizing is a process in which the textile yarn is subjected to anair jet that impinges on its surface to make the yarn “fluffy”. The airjet causes the surface filaments to break at random, giving the yarn abulkier appearance. The extent to which this occurs can be controlled bythe velocity of the air jet and the yarn feed rate. An equivalent effectcan be produced by electrostatic or mechanical manipulation of thefibers, yarns or roving.

Fabric Design

The fabric pattern, often called the construction, is an x, y coordinatesystem. The y-axis represents warp yarns and is the long axis of thefabric roll (typically 30 to 150 m, or 100 to 500 ft.). The x-axis isthe fill direction, that is, the roll width (typically 910 to 3050 mm,or 36 to 120 in.). Basic fabrics are few in number, but combinations ofdifferent types and sizes of yarns with different warp/fill counts allowfor hundreds of variations.

Basic fabric structures include those made by woven, non-woven and knitprocesses. In this invention, one preferred design is a knit structurein which both the x axis strands and the y axis strands are heldtogether with a third strand or knitting yarn. This type of knitting isweft-inserted-warp knitting. If an unshifted tricot stitch is used, thex and y axis strands are the least compressed and, therefore, give thebest coverage at a given areal weight. This structure's coverage can befurther increased, i.e., further reduction in porosity, by usingnear-zero-twist-yam or roving which, naturally, spreads more thantightly twisted yarn. This design can be further improved by assistingthe spreading of filaments by mechanical (needling) means, or byhigh-speed air dispersion of the filaments before or after fabricformation.

The most common weave construction used for everything from cottonshirts to fiberglass stadium canopies is the plain weave. The essentialconstruction requires only four weaving yarns: two warp and two fill.This basic unit is called the pattern repeat. Plain weave, which is themost highly interlaced, is therefore the tightest of the basic fabricdesigns and most resistant to in-plane shear movement. Basket weave, avariation of plain weave, has warp and fill yarns that are paired: twoup and two down. The satin weave represent a family of constructionswith a minimum of interlacing. In these, the weft yarns periodicallyskip, or float, over several warp yarns. The satin weave repeat is xyarns long and the float length is x−1 yarns; that is, there is only oneinterlacing point per pattern repeat per yarn. The floating yarns thatare not being woven into the fabric create considerable loose-ness orsuppleness. The satin weave produces a construction with low resistanceto shear distortion and is thus easily molded (draped) over commoncompound curves. Satin weaves can be produced as standard four-, five-,or eight-harness forms. As the number of harnesses increases, so do thefloat lengths and the degree of looseness making the fabric moredifficult to control during handling operations. Textile fabricsgenerally exhibit greater tensile strength in plain weaves, but greatertear strength in satin weaves. The higher the yarn interlacing (for agiven-size yarn), the fewer the number of yarns that can be woven perunit length. The necessary separation between yarns reduces the numberthat can be packed together. This is the reason for the higher yarncount (yarns/in.) that is possible in unidirectional material and itsbetter physical properties.

A plain weave having glass weft and warp yarns or roving, in a weaveconstruction is known as locking leno. The gripping action of theintertwining leno yarns anchors or locks the open selvage edges producedon rapier looms. The leno weave helps prevent selvage unraveling duringsubsequent handling operations. However, it is also valuable where avery open (but stable) weave is desired.

The preferred “leno weave” fabric 100 of this invention consists of weftyarns 10 and warp yarns 12. The weft yarns 10 are oriented in thecross-machine direction and the warp yarns 12 are oriented in themachine direction 10. As shown in FIGS. 1 and 2, the weft yarns 10 andwarp yarns 12 are twisted around one another at regular intervals andare locked in place. Preferably, the spacing between yarns is fairlyopen with hole sizes ranging in area from 0.02 to more than 4.0 squareinches (0.5-102 mm²). The leno weave 100 can be converted into a“thickened” fabric 101.

One of the important features of the present invention is demonstratedin FIG. 3 in which alternate weft yarns 10A and 10B are shown assuming agenerally sinusoidal profile when viewed in the plain of the fabric, andmore preferably, the weft yarns alternate between sinusoidal profileshaving at least two different orientations represented by weft yarns 10Aand 10B, for example. Preferably, the thickened fabric has an enhancedthickness of at least about 1 mm, preferably greater than 10 mm, and insome cases, greater than 500 mm. Experience has proven that suchthicknesses are rarely achievable in a cost effective way utilizingglass yarns employing the normal means of fabric formation. Byexploiting the nature of specific weave constructions, such as a lenoweave, and by coating and drying the product on a tenter frame, wherebythe width of the fabric can be controlled, the preferred thickenedfabric 101 or thickened fabric structure 30 can be produced in acontrolled and repeatable way.

In a first embodiment of producing a thickened fabric 101 of thisinvention, the warp yarns of the leno weave 100 are subjected to atensile force. The warp yarns 12 then begin to untwist themselves,creating a torque effect on the weft yarns 10A and 10B, for example. Aseach warp yarn 12 untwists, the combined torque effect creates a weftyarn 10A or 10B that assumes a sinusoidal profile when viewed in theplane of the fabric. See FIG. 3. The thickness of the fabric as measuredfrom the high point and low point of the sinusoidal profiles of weftyarns 10A and 10B thus increases with a slight loss in the width of thefabric.

It has been determined that the thickness increase of the leno weave 100should be fixed in some method, such as by using a binder or coating. Ithas been helpful to use a polymeric resin 15, as shown in the explodedview FIG. 4, which is coated and dried on a preferred tenter frame 105equipped with clips, as shown in FIG. 5. The tenter frame 105 functionsto apply the necessary tension to the warpulence of the fabric to inducethe torquing effect. The clips hold the edges of the fabric as it runsthrough the coating line and drying oven (not shown), and are adjustableto add or subtract fabric width as needed. Applying high tension,allowing the width of the leno fabric 100 to decrease by the use ofclips can increase the thickness of the fabric via the torque effect onthe weft yarns created by the tensile force applied to the warp yarns12. Although tenter frames equipped with clips 105 have been useful inpracticing this invention, this invention is not so limited. “Clipless”drying systems can be used with some greater variation in the weft andthickness of the fabric. It is also believed that the magnitude of thethickness can be further enhanced by other means. One such method is tocreate a fabric with an “unbalanced” construction, such that thecombined weight of the warp yarns is greater than the combined weight ofthe weft yarns. The ability of the weft yarns to resist deformation dueto torque is thus reduced. Another way to accomplish greater thicknessin the substrates of this invention is to use a heavier warp yarn, butless of them in the warp direction. This results in a greater amount oftension per warp yarn and a wider span of weft yarn to be acted upon.The torque effect will increase with its accompanying increase in fabricthickness.

The design of glass fabrics suitable for this invention begins with onlya few fabric parameters: type of fiber, type of yarn, weave style, yarncount, and areal weight.

Fiber finish is also important because it helps lubricate and protectthe fiber as it is exposed to the sometimes harsh weaving operation. Thequality of the woven fabric is often determined by the type and qualityof the fiber finish. The finish of choice, however, is usually dictatedby end-use and resin chemistry, and can consist of resinous materials,such as epoxy.

The following fabric styles and categories are useful in the practice ofthis invention: Areal wt. Fabric grams/m² oz/yd² Light weight 102-340 3-10 Intermediate weight 340-678 10-20 Heavy weight  508-3052 15-90

Thickness Fabric μm mil Light weight  25-125 1-5 Intermediate weight125-250  5-10 Heavy weight 250-500 10-20

It has been determined that fabrics having an areal weight of about15-500 grams/m² and thicknesses of about 0.025-0.25 inches are mostpreferred.

Increasing the thickness of the fabric 100 of this invention, withoutsignificantly adding to the cost can provide a fabric with goodlongitudinal strength/stiffness values, as well as transverse (filldirection) toughness and impact resistance. The ability to thicken afabric allows it to be used in many end-uses, such as reinforcement forcomposites, housings, ballistic applications, aerospace and automotiveapplications, gypsum and cement boards, concrete reinforcement, etc.

It is also possible to “teach” the looms new tricks, particularly inthree-directional weaving, but interesting modifications are evenpossible for two-directional fabric. The loom has the capability ofweaving an endless helix using different warp and fiber fill.Alternatively, a glass textile roving warp or weft, such as E-glass yarnand olefin warp weft, such as polyethylene or polystyrene fiber, can beused. Alternatively, blends such as Twintex® glass-polyolefin blendsproduced by Saint-Gobain S.A., Paris, France, or individual multiplelayers of polymers, elastomerics, rayon, polyester and glass filamentscan be used as roving or yarn for the facing material, or as additionalbonded or sewn layers of woven, knitted felt or non-woven layers.

A typical binder/glass fiber loading is about 3-30 wt %. Such bindersmay or may not be a barrier coating. These binders also may or may notcompletely coat the exterior facing fibers. Various binders areappropriate for this purpose, such as, for example, phenolic binders,ureaformaldehyde resin, or ureaformaldehyde resin modified with acrylic,styrene acrylic, with or without carboxylated polymers as part of themolecule, or as a separate additive. Additionally, these binders can beprovided with additives, such as UV and mold inhibitors, fireretardants, etc. Carboxylated polymer additions to the binder resin canpromote greater affinity to set gypsum, or to Portland cement-, forexample, but are less subjected to blocking than resins without suchadditions. One particularly desirable binder resin composition is a 70wt % ureaformaldehyde resin-30 wt % styrene acrylic latex or an acryliclatex mixture, with a carboxylated polymer addition.

The fabric 101 or thickened fabric 30 of this invention can be furthertreated or coated with a resinous coating 15 prior to use, to help fixthe weft fibers 10 a and 10 b in a preferred sinusoidal pattern, asshown in FIGS. 3 and 4. Resinous coatings 15 are distinguished from thesizing or binder used to bond the fibers together to form the individuallayers, as described above. Coatings 15 can include those described inU.S. Pat. No. 4,640,864, which is hereby incorporated herein byreference, and are preferably alkali-resistant, water-resistant and/orfire-retardant in nature, or include additives for promoting saidproperties. They are preferably applied during the manufacture of thefabric 101 or thickened fabric 30.

The coating 15 applied to the fabric 101, as shown in FIG. 4, of thisinvention preferably coats a portion of the fibers and binds the yarns10 and 12 together. Alternatively, the coating 15 can increase ordecrease the wetting angle of the matrix to reduce penetration into theyarns or increase adhesion. The coating 15 can further contain a UVstabilizer, mold retardant, water repellant, a flame retardant and/orother optional ingredients, such as dispersants, catalysts, fillers andthe like. Preferably, the coating 15 is in liquid form and the fabric101 is led through the liquid under tension, such as by a tenter frame105, or the liquid is sprayed (with or without a water spray precursor)on one or both sides of the fabric 101. Thereafter, the fabric 101 maybe squeezed and dried.

Various methods of applying the liquid may be used, includingdip-coaters, doctor blade devices, roll coaters and the like. Onepreferred method of treating the fabric 101 with the resinous coatings15 of this invention is to have a lower portion of one roll partiallysubmerged in a trough of the liquid resinous composition and the fabric101 pressed against the upper portion of the same roller so that anamount of the resinous composition is transferred to the fabric 101. Thesecond roller above the first roller controls the movement of the fabric101 and the uniformity of the amount of resinous coating 15 disposedthereon. Thereafter, the coated fabric 101 is led in a preferred methodto steam cans to expedite drying. It is preferred to pass the coatedfabric over steam cans at about 250-450° F. (100-200° C.) which drivesthe water off, if a latex is used, and additionally may cause some flowof the liquid resinous material to further fill intersticies betweenfibers, as well as coat further and more uniformly fibers within thefabric 101. The coating preferably covers about 50-80% of the surfacearea targeted, more preferably about 80-99% of said area.

The preferred resinous coatings 15 of this invention can contain aresinous mixture containing one or more resins. The resin can containsolid particles or fibers which coalesce or melt to form a continuous orsemi-continuous coating which substantially prevents the penetration ofliquid moisture, which can be alkaline. The coating can be applied invarious thicknesses, such as for example, to sufficiently cover thefibrous constituents of the fabric 100 so that no fibers protrude fromthe coating 15, or to such a degree that some of the fibers protrudefrom the coating 15.

The coating 15 of this invention can be formed substantially by thewater-resistant resin, but good results can also be achieved by formingthe coating or saturant from a mixture of resin and fillers, such assilicates, silica, gypsum, titanium dioxide and calcium carbonate. Thecoating 15 can be applied in thermoplastic, latex or curablethermosetting form. Acceptable resins include pvc plastisol,styrene/butadiene (such as BASF ND 5600) and styrene/acrylic copolymer,acrylics (such as Paranol SA200 or Rohm & Haas GL 618), flame retardantacrylics or brominated monomer additions to acrylic, such as PyropolyAC2001, poly(vinyl acetates), poly(vinyl alcohols), vinylidene chloride,siloxane, and polyvinylchloride such as Vycar® 578. Thermosettingresins, such as vinyl esters, epoxy or polyester, could also be used forhigher strength and rigidity. In addition, fire retardants, such asbromated phosphorous complex, halogenated paraffin, colloidal antimonypentoxide, borax, unexpanded vermiculite, clay, colloidal silica andcolloidal aluminum can be added to the resinous coating or saturant.Furthermore, water resistant additives can be added, such as paraffin,and combinations of paraffin and ammonium salt, fluorochemicals designedto impart alcohol and water repellency, such as FC-824 from 3M Co.,organohydrogenpolysiloxanes, silicone oil, wax-asphalt emulsions andpoly(vinyl alcohol) with or without a minor amount a minor amount ofpoly(vinyl acetate). Finally, the coatings 15 can include pigment, suchas kaolin clay, or lamp black thickeners.

Example A

This trial was undertaken to prove the efficacy of inducing significantthickness increases (in the “Z” plane) into an open, leno weave fabricof unbalanced construction.

When the collective weight of warp yarns significantly outweighs that ofthe weft yarns, a noticeable torque effect is induced in the warp yarnswhen under tension on the finishing machines. The torque effect causesthe weft yarns to deform in a sinusoidal fashion across the width of theweb, and thus the fabric thickness increases.

Calculations have shown that a fabric based on existing fabric style No.0061 by Saint-Gobain Technical Fabrics, St. Catharines, Ontario, Canada,will serve as a useful starting point for development in that it hasapproximately the right construction and cost. The 0061 fabric wasmodified to unbalance the construction by replacing the 735 tex weftyarn with a 275 tex yarn. This both reduces the fabric cost and helpedensure that the torque effect would be observed. A stiff, inexpensiveSBR (styrene-butadiene rubber) latex was selected (style 285) for thecoating as it has the advantage of: low cost; alkali resistance; theexcellent toughness needed to bond the open fabric. Frame D was selectedas the finishing machine for two reasons: it is capable of coating two1.2 meter panels side-by-side; and the clips of the tenter frame 105would serve to control the width of the fabric as the torque effecttakes place. Without the clips, it is expected that the width of thefabric would be difficult to control on the finishing line.

Results and Recommendations

It was found that the thickness of the fabric could be increased 0.5-100times that of the same fabric without the torque effect. The observedincrease was a 2.7 times increase, from 0.54 mm to 1.46 mm. This wasaccomplished by applying the highest amount of tension possible to thefabric on Frame D, and then slowly decreasing the width of the clips.The fabric width decreased from 2465 mm to 2380 mm (about 3.4%), whichis a loss of 85 mm (3.3 inches). The fabric was not unduly distorted bythe process, and with some fine-tuning the quality should be acceptable.Two rolls of 45.7 meter length and two of 30 meter length of theenhanced thickness fabric were produced.

Details of Trial Machine: frame D Line Speed:  25 meters/min Oven Temp:185/185° C. Winder: center wind Let-off pressure: 140 psig Front outputpress.:  8 psig Tension:  15 Clip spacing:  93 inches

Fabric Analysis Finished Width of one panel:  1190 mm (1202 mm includingfringe edge). Yarn Count: 20.64 × 10.0 ends/picks per 10 cm CoatedFabric Weight: 113.4 grams/m2 Coating Add-on: 31.9% Thickness:  1.46 mm(0.058 inches)

From the foregoing, it can be realized that this invention providesthicker fabrics and methods for their manufacture. These fabrics willhave greater ability to reinforce matrices in a vertical or “Z”direction, without substantially increasing the cost of thereinforcement. Although various embodiments have been illustrated, thiswas for the purpose of describing, and not limiting, the invention.Various modifications, which will become apparent to one skilled in theart, are within the scope of the invention described in the attachedclaims.

1. A fabric comprising: an oriented layer containing polymeric or glassfibers wherein said at least a portion of said fibers are mechanicallymanipulated to increase the layer's thickness by at least about 50%; anda polymeric coating disposed over at least a portion of said fibers soas to retain said layer's increased thickness.
 2. The fabric of claim 1wherein said porous containing layer comprises a woven or non-wovenfabric, scrim, mesh, or a combination thereof.
 3. The fabric of claim 1wherein said porous layer comprises an open woven fabric comprising highstrength, weft and warp yarns containing glass fibers.
 4. The thickenedfabric of claim 1 wherein said fibers are mechanically manipulated toincrease the layer's thickness by at least about 100%.
 5. The fabric ofclaim 1 wherein said polymeric coating comprises a polymeric resin forsubstantially binding said fibers.
 6. A corrosion-resistant fabric foruse as a reinforcement in a matrix, comprising: an open, woven,scrim-type or knitted fabric comprising high strength, non-metallic weftand warp yarns, whereby a portion of said yarns are mechanicallymanipulated to increase the fabric's thickness by at least about 50%,and a bonding agent for retaining said weft and warp yarns in arelatively fixed position.
 7. The fabric of claim 6 wherein said fabriccomprises a leno weave.
 8. The fabric of claim 7 wherein said weft andwarp yarns are spaced apart by at least about 1 mm.
 9. The fabric ofclaim 7 wherein said bonding agent comprises a polymeric resin forsubstantially binding said yarns.
 10. The fabric of claim 7 wherein saidwarp yarns are subjected to a tensile force which causes said weft yarnsto become undulated to a height of at least 1 mm.
 11. The fabric ofclaim 7 wherein said warp yarns have a combined weight which is greaterthan the combined weight of the weft yarns.
 12. The fabric of claim 7wherein a portion of said warp yarns are heavier than a portion of saidweft yarns, said warp yarns are fewer in number than said weft yarns, orboth.
 13. A matrix reinforcement comprising: an open, woven fabriccomprising weft and warp yarns containing non-metallic fibers, whereby aportion of said weft yarns are undulated, relative to said warp yarns,resulting in an increased thickness for said fabric; said fabric coatedwith a polymeric resin for substantially binding said weft yarns in saidundulated condition.
 14. The reinforcement of claim 13 wherein saidpolymeric resin comprises styrene butadiene rubber, acrylic, styreneacrylic, or combinations or derivatives thereof.
 15. The reinforcementof claim 14 bonded to a matrix comprising an organic or inorganicmaterial.
 16. The reinforcement of claim 14 wherein said undulated weftyarns comprise a substantially regular sinusoidal-like pattern.
 17. Thereinforcement of claim 14 wherein alternative ones of said weft yarns ofsaid fabric have different sinusoidal-like patterns which are notoverlapping when observed from the plane of the fabric.
 18. A method ofmaking a fabric having increased thickness comprising: (a) providing ascrim-type, braided, woven or knitted fabric comprising weft and warpyarns containing glass fibers; (b) applying a tensile force to said warpyarns, whereby a portion of said weft yarns become undulated resultingin an increased thickness for said fabric; and (c) binding said fabricwith a bonding agent whereby said undulated weft yarns becomesubstantially fixed.
 19. The method of claim 18 wherein said providingstep (a) provides weft and warp yarns containing different weights,different numbers of fiber, or a combination thereof.
 20. The method ofclaim 19 wherein said binding step (c) comprises applying said bondingagent to the cross over points between said weft and warp yarns.
 21. Themethod of claim 19 wherein said applying a tensile force step (b)comprises employing a tenter frame to apply tension to said warp yarns.22. The method of claim 19 wherein said applying a tensile force step(b) includes providing a sinusoidal shape to at least a portion of saidweft yarns.
 23. The method of claim 22 wherein said binding step (c)substantially fixes said sinusoidal shape.
 24. The method of claim 19wherein said glass fibers contain E glass, C glass, S glass, or AR glasscompositions, or a combination thereof.
 25. A composite comprising amatrix reinforced with the fabric of claim
 1. 26. A compositecomprising: a matrix and reinforcement joined to said matrix, saidreinforcement including a woven, braided, knitted or scrim-type fabric,said fabric including high strength, non-metallic weft and warp yarns,whereby a portion of said yarns are undulated to a height of at least 1mm and fixed by a resinous bonding agent.
 27. The composite of claim 26wherein said matrix comprises an organic or inorganic composition.
 28. Abuilding material comprising the composite of claim
 26. 29. A polymermatrix composite comprising the composite of claim 26 embedded within apolymer matrix.
 30. A soil reinforcement system comprising the compositeof claim 26 embedded within a soil matrix.
 31. A road reinforcementcomprising the composite of claim 26 disposed below a road composition.32. A cement or gypsum board comprising a cement or gypsum core facedwith the composite of claim
 26. 33. A cement or gypsum board comprisinga cement or gypsum core and the composite of claim 26 embedded therein.34. A water drainage system comprising the composite of claim
 26. 35. Aroofing membrane or shingle comprising the composite of claim
 26. 36. Atextile product comprising the composite of claim
 26. 37. A cast forinjured bones or joints comprising a resin and the composite of claim 26embedded therein.